1. Field of the Invention
This invention generally relates to electric discharge lamps and has particular reference to a method of forming the envelope for an improved fluorescent lamp of compact size and high brightness that is suitable for use as a light source in various kinds of residential and commercial lighting fixtures that are designed for incandescent type lamps.
2. Description of the Prior Art
Electric discharge lamps having tubular envelopes which provide "three-dimensional" type light sources are generally well known in the art. U.S. Pat. No. 2,652,483 granted Sept. 15, 1953 to Laidig et al. discloses fluorescent lamp units of helical configuration (FIGS. 7 and 15 embodiments) that are formed by coupling several semi-circular lamps together to form one operative assembly. Another fluorescent lamp of three-dimensional configuration that is formed by four sections of conventional fluorescent lamp tubing which are "bundled" together and interconnected by suitable apertures in the side walls of the respective tubes is disclosed in U.S. Pat. No. 3,501,662 issued Mar. 17, 1970 to Plagge.
Electric discharge lamps having tubular envelopes that are bent into various shapes to provide concentrated light sources are also known in the art. A double-ended type sodium-vapor discharge lamp having an envelope which is formed from a single tube that is folded or bent upon itself twice to provide three straight tubular segments that are disposed in parallel triangular-spaced relationship is disclosed in British Pat. No. 854,745 published Nov. 23, 1960 (FIGS. 3 and 4 embodiment). A luminous discharge tube designed for advertising and display purposes (or as a beacon light) and having an envelope formed from glass tubing which is bent upon itself eleven times to provide a corresponding number of U-shaped sections is disclosed in U.S. Pat. No. 1,898,615 granted Feb. 21, 1933 to Byrnes. Gaseous discharge devices consisting of a heat-conserving housing that encloses a lamp having a tubular envelope that is bent upon itself three times to provide four straight sections which are spaced from one another and arranged so that the electrode-containing ends of the envelope are located on opposite sides of one of the curved segments or bends is disclosed in U.S. Pat. Nos. 2,001,511 and 2,200,940 granted to Uyterhoeven et al.
In accordance with the more recent proposal, a screw-in type flourescent lamp of compact size is provided by suitably partitioning the interior of a cylindrical envelope or by making the envelope from tubing that is bent upon itself to provide a U-shaped bulb, and which may be additionally twisted into spiral shape or redoubled on itself to provide a generally M-shaped envelope. A fluorescent lamp constructed in this manner is disclosed in U.S. Pat. No. 3,551,736 granted Dec. 29, 1970 to Doehner (the M-shaped tubular envelope embodiment being shown in FIG. 5 and described along with the other aforementioned shapes at lines 24-30, column 2).
A method of making a circular-shaped fluorescent lamp by bending a straight tubular glass envelope around a suitable curved jig is disclosed in U.S. Pat. No. 3,993,465 granted Nov. 23, 1976 to Hurx et al.